This invention relates generally to the upgrading of hydrocarbon feed materials and, more particularly, to the processing of petroleum or other oils, such as in the manufacture of lubricating oils.
Most petroleum oils generally contain waxes which, at low temperatures, come out of solution and interfere with the flow of the oil. To produce an oil having satisfactory low temperature flow properties, such oils are typically processed to remove at least some of such wax materials. An analytical measurement for the low temperature flow property of an oils is "pour point," ASTM D-97/C-708. Oils containing relatively greater amounts of wax materials will typically have relatively higher pour point temperatures, that is, waxes will more readily form therefrom as the temperature is reduced.
The process for removing waxes, or high pour molecules, from lubricating oils (commonly referred to as "lube oils") is commonly referred to as "dewaxing." Processes for the manufacture of lubricating oils and involving dewaxing typically involve a trade-off between lube oil yield and pour point. That is higher lube oil yields can be realized at the expense of impairing product pour point and higher pour point products can be obtained at the expense of reducing lube oil yields.
In one technique of dewaxing, the oil is mixed with a solvent that is miscible with the oil but a poor solvent for the wax material. The solvent solution is than chilled, with wax material coming out of solution and subsequently being filtered from the oil.
Solvent dewaxing has been combined with various processing techniques in an attempt to produce products having desired properties. For example, U.S. Pat. Nos. 4,822,476 (Ziemer et al.) and 4,867,862 (Ziemer) disclose processes for hydrodewaxing and hydrofinishing a hydrocracked, solvent dewaxed lube oil base stock utilizing a single stage, multilayered catalyst system. In the first layer, the solvent dewaxed stock is catalytically dewaxed. In the second layer, the catalytically dewaxed material is hydrofinished. These patents report no appreciable change in viscosity, Viscosity Index (VI) or pour point relative to the use of the hydrofinishing catalyst alone.
In recent years, workers in the field have proposed various processes for the catalytic dewaxing of petroleum oils. In the preparation of lubricating oils and the like from hydrocarbon feeds, catalytic dewaxing processes have been combined with hydrotreating, hydrocracking and/or various solvent extraction steps to obtain products having desired properties. Hydrocracking and/or solvent extraction steps can be conducted prior to catalytic dewaxing to remove components such as metal-containing feed components, asphaltenes and polycyclic aromatics having properties that differ grossly from those desired. In particular, solvent extraction can be conducted to remove polycyclic aromatic feed components and nitrogen-containing cyclic components, removal of the latter typically having particular importance in order to avoid poisoning of the catalyst used for the catalytic dewaxing. Hydrotreating under mild or severe conditions can follow the catalytic dewaxing operation and can serve to improve the oxidation stability and reduce the nitrogen and sulfur content of the lube oil.
As one example of a process for producing lube oils in which a catalytic dewaxing step is included as part of a multistep process, U.S. Pat. No. 4,597,854 (Penick) discloses a process which employs alternating beds of dewaxing and hydrogenation catalysts to allegedly decrease coke deposits. In the disclosed process, the feedstock is contacted at elevated temperature with a first medium pore crystalline zeolite (such as the Group VIII metal-containing composition, Ni-ZSM-5) catalyst bed in the presence of hydrogen, subsequently contacting the partially dewaxed effluent from the first bed with at least one separate hydrogenation catalyst bed under hydrotreating conditions followed by further dewaxing the hydrotreated feedstock in at least one additional catalytic dewaxing bed and further hydrogenating the further dewaxed material in an additional hydrotreating step.
As further examples of multistep processes for preparation of lube oils, U.S. Pat. No. 4,259,170 (Graham et al.) discloses a process that includes a combination of both catalytic dewaxing and solvent dewaxing steps. According to a more specific aspect of Graham et al., the process includes a solvent extraction step prior to a dewaxing step wherein any suitable solvent, such as furfural, phenol, chlorex, nitrobenzene, or N-methyl-pyrrolidone is used.
U.S. Pat. No. 4,259,174 (Chen et al.) discloses a process comprising solvent extraction followed by catalytic dewaxing.
U.S. Pat. No. 4,283,272 (Garwood et al.) discloses preparation of lube oils by a process that includes hydrocracking, catalytic dewaxing and hydrotreating steps.
U.S. Pat. No. 4,292,166 (Gorring et al.) discloses a combination process wherein a dewaxing step is carried out prior to a hydrocracking step. Specifically, a hydrocarbon oil feed selected from the group consisting of vacuum gas oils, deasphalted oils and mixtures thereof is converted to a low pour point, high VI lube base stock by first dewaxing the feed in the presence of hydrogen and a dewaxing catalyst comprising a zeolite having a Constraint Index of 1 to 12, followed by contacting the dewaxed feedstock and hydrogen with a hydroconversion catalyst comprising a platinum group metal and a zeolite having a silica to alumina ratio of at least 6. Gorring et al. also contemplates interposing a conventional hydrotreating step between catalytic dewaxing and the hydrocracking step when the feed to the process contains high levels of deleterious nitrogen compounds.
A combination process is also disclosed in U.S. Pat. No. 4,358,363 (Smith) wherein a fuel oil, containing impurities deleterious to the catalyst, is first treated with a sorbent comprising a first molecular sieve zeolite having pores with an effective diameter of at least about 5 Angstroms under sorption conditions followed by a treatment with a dewaxing catalyst comprising a second molecular sieve zeolite having pores with an effective diameter of at least about 5 Angstroms and equal to or smaller than the effective diameter of the pores of the first molecular sieve zeolite. In a more specific aspect of the disclosure, the first and second molecular sieves have the same crystal structure wherein the Constraint Index is 1 to 12 and the dried hydrogen form crystal density is less than about 1.6 grams per cubic centimeter. Patentee indicates that the effectiveness of the dewaxing catalyst is increased when catalyst poisons, speculated to be basic nitrogen compounds and oxygen and sulfur compounds, are removed.
The teachings of U.S. Pat. No. 4,282,085 (O'Rear et al.) likewise appreciate the deleterious effect of nitrogen-containing impurities on ZSM-5 type crystalline aluminosilicate-containing catalysts. Specifically, patentees disclose a process for upgrading a petroleum distillate feed with a catalyst comprising ZSM-5 type zeolite possessing no hydrogenation activity wherein the feed has a content of nitrogen-containing impurities below about 5 ppm, calculated by weight as nitrogen. The low-nitrogen feedstock results in a lower deactivation rate for the catalyst.
U.S. Pat. No. 4,153,540 (Gorring et al.) discloses a process for upgrading full range shale oil. More specifically, patentees' process involves contacting the full range shale oil with a hydrotreating catalyst and hydrogen in order to convert organic compounds of sulfur, nitrogen, oxygen, and metal. The effluent from the hydrotreater is then passed to a dewaxing zone and contacted with dewaxing catalyst at conversion conditions calculated to hydrodewax the shale oil and convert at least 50% of the shale oil boiling above about 750.degree. F. to reaction products boiling below 750.degree. F.
U.S. Pat. No. 4,181,598 (Gillespie et al.) discloses a process for the manufacture of lube base stock oil wherein a waxy crude oil fraction is solvent refined and then catalytically dewaxed. The dewaxing catalyst is disclosed as a composite of hydrogenation metal, preferably a metal of Group VIII of the Periodic Table, associated with the acid form of an aluminosilicate zeolite having a silica/alumina ratio of at least about 12 and a constrained access to the intracrystalline free space. The effluent of catalytic dewaxing is then cascaded into a hydrotreater containing, as a catalyst, a hydrogenation component on a nonacidic support, such as cobalt-molybdate or nickel-molybdate on alumina.
Of the various solvent extraction processes, the most prevalent solvent employed is phenol. Other solvents employed include low boiling point autorefrigerative hydrocarbons, such as propane, propylene, butane, pentane, etc., liquid sulfur dioxide, furfural, and N-methyl-2-pyrrolidones (NMP). NMP is a preferred solvent because it is less toxic in relation to the above-mentioned solvents and requires less energy to effect the extraction.
Generally, when the solvent-extracted raffinate base stocks are dewaxed with a shape-selective molecular sieve, the Viscosity Index (VI) of the product oil is reduced to a greater extent than if the same stocks were solvent dewaxed. This is because shape-selective dewaxing catalysts reduce pour point by cracking normal and near normal paraffins which results in a high concentration of low VI possessing aromatics in the product oil. As a result of having a relatively higher selectivity for cracking normal paraffins versus cracking isoparaffins, some shape-selective molecular sieves are more selective than others in retaining high VI isoparaffins in the oil during dewaxing. For instance, even though the borosilicate molecular sieve disclosed in U.S. Pat. No. 4,269,813 (Klotz) falls in the category of high VI selective catalysts, the VI loss relative to solvent dewaxing is in the range of 8-12 VI units when compared to phenol-extracted SAE 10 raffinate. This loss would have to be compensated for by more severe solvent extraction of aromatics, which is expensive and energy-consuming.
The loss in VI attributed to catalytic hydrodewaxing in comparison to solvent dewaxing is also noted in a paper entitled "Hydrodewaxing of Fuels and Lubricants using ZSM-5 Type Catalysts," by R. G. Graven and J. R. Green, presented at the Australian Institute of Petroleum's 1980 Congress. Therein it is mentioned that the VI for neutral distillate charge stocks dewaxed in the presence of a ZSM-5 catalyst is lower by 3 to 8 units than comparable quality solvent-dewaxed neutrals.
In a paper entitled "Low-Temperature Performance Advantages for Hydrodewaxed Base Stocks and Products," by C. N. Rowe and J. A. Murphy, presented at the 1983 NPRA annual meeting, it is also pointed out that the VI differential between the catalytic dewaxing process disclosed therein and conventional solvent dewaxing ranges between 6 an 10 units for light neutral feedstocks to little or no difference for bright feedstocks.
We have observed that not all solvent raffinates can be subsequently catalytically dewaxed on an equivalent basis. In particular, the high-nitrogen content levels, particularly basic nitrogen compounds, in certain solvent-extracted raffinates are believed to be responsible for the rapid deactivation of the dewaxing catalysts.
For instance, we have found NMP-extracted raffinates to be substantially more difficult to dewax over a shape-selective dewaxing catalyst, i.e., such catalysts typically suffer from a higher deactivation rate when used in the treatment of NMP-extracted raffinates as compared to phenol-extracted raffinates.
In addition, a number of patents and other documents relate to dewaxing of oils using various catalytic materials. For example, U.S. Pat. No. Re. 28,398 (Chen et al.) relates to the dewaxing of oils by shape-selective cracking and hydrocracking over ZSM-5 type zeolites. U.S. Pat. No. 4,360,419 (Miller) discloses a catalytic dewaxing process using a CZH-5 zeolite having a hydrogenation component. U.S. Pat. No. 4,869,806 (Degnan et al.) discloses a catalytic dewaxing process utilizing ZSM-57 as the catalyst. U.S. Pat. Nos. 4,589,976 (Zones); 4,610,854 (Zones); and 4,826,667 (Zones) disclose the use of zeolites SSZ-16, SSZ-15, and SSZ-25, respectively, in hydrocarbon processing, including dewaxing. European Patent Application 0 321 061 discloses catalytic dewaxing of a wax-containing hydrocarbon oil utilizing a crystalline gallium silicate. European Patent Application 0 243 129 discloses selective cracking of a paraffinic hydrocarbon feed using a tectometallosilicate of the Theta-1 type loaded with Re, Ni, Pd or Pt to produce unsaturated hydrocarbons. European Patent Application 0 187 496 discloses a method of preparing gallosilicate zeolites and the use of the catalysts so prepared in various processing schemes including hydrocracking and pour point reduction.
Despite the plethora of catalytic dewaxing processes disclosed in the prior art, there is still the need for an improved catalytic dewaxing process. More specifically, there is a need for a catalytic dewaxing process wherein the yield and viscosity index of the liquid product are increased for a given level of product pour point reduction.
In connection with the present invention, it should be noted that catalysts containing an AMS-type borosilicate molecular sieve coupled with catalytic metal components are known.
For instance, commonly assigned U.S. Pat. No. 4,434,047 (Hensley, Jr. et al.) discloses a catalytic dewaxing hydrotreating process using a catalyst containing a shape-selective zeolite cracking component such as an AMS-type borosilicate molecular sieve, and a hydrogenating component containing Cr, at least one other Group VIB metal and at least one Group VIII metal.
U.S. Pat. No. 4,268,420 (Klotz) similarly discloses an AMS-type crystalline borosilicate which can be used in intimate combination with a hydrogenating component, such as tungsten, vanadium, molybdenum, rhenium, nickel, cobalt, chromium, manganese, or a noble metal, such as platinum or palladium, or rare earth metals, where a hydrogenation-dehydrogenation function is to be performed. The hydrogenation metal can be impregnated on the borosilicate or on a support comprising the crystalline borosilicate suspended in and distributed throughout a matrix of a porous refractory inorganic oxide.
In addition, commonly assigned U.S. Pat. Nos. 4,560,469 (Hopkins et al.) and 4,563,266 (Hopkins et al.) both relate to catalytic dewaxing processes utilizing catalytic compositions comprising a crystalline borosilicate molecular sieve and a hydrogenation component. In '469 the hydrogenation component consists essentially of nickel and in '226 the hydrogenation component includes at least one Group VIII noble metal.
Also, commonly assigned U.S. Pat. Nos. 4,636,299 (Unmuth et al.), 4,728,415 (Unmuth et al.) and 4,755,279 (Unmuth et al.) relate to processes for the manufacture of lubricating oils wherein hydrotreating is followed by treatment in the presence of a dewaxing catalyst composition containing borosilicate molecular sieve. In one specific aspect of the '299 patent, hydrotreatment is preceded by solvent extraction with N-methyl-2-pyrrolidone (NMP) to extract a portion of the aromatic compounds contained in the feed. In one specific embodiment of the '415 patent, the borosilicate molecular sieve is on a silica-alumina-containing matrix and the catalyst composition also contains at least one hydrogenation component from the Group VIB or Group VIII metals. In one specific embodiment of the '279 patent, the catalyst composition contains at least one hydrogenation component of platinum or palladium.
Each of these patents disclose a catalyst composition comprising a borosilicate molecular sieve and a Group VIB or Group VIII hydrogenation metal ('299 and '415 patents) or platinum or palladium ('279 patent). These patents teach that the sequence or order of addition of the respective catalyst components is not critical as these patents contemplate the use of catalysts in which the hydrogenating component is dispersed on the molecular sieve component or on a molecular sieve-matrix component dispersion or on the matrix component of a molecular sieve-matrix dispersion. These patents disclose that the catalyst of each patent can be employed in suitable forms such as spheres, extrudate, pellets, C-shaped or clover leaf-shaped particles.
These patents do not teach, disclose or suggest the use or desirability of a catalytic hydrodewaxing zone having separate sections of two different functioning materials (e.g., cracking function material and hydrogenation function material).
In a paper, entitled "Stepwise Reaction via Intermediates on Separate Catalytic Centers," P. B. Weisz, Science, Vol. 123 (1956), pp. 887 through 888, a general criterion for the physical proximity required between two types of catalytic materials was proposed for physical transport processes in heterogenous catalysis systems. According to the paper, the proximity is dependent on the maximum attainable vapor pressure of the intermediate. In a subsequent paper, entitled "Stepwise Reaction on Separate Catalytic Centers: Isomerization of Saturated Hydrocarbons," Science, Vol. 126 (1957), pp. 31 through 32, P. B. Weisz et al., reported on work done on catalytic isomerization of paraffin hydrocarbons by acidic solids (e.g., aluminum silicates) impregnated with small amounts of Pt. For the maximum reaction rate for the conversion of n-heptane to iso-heptanes using such materials, the diffusion criterion discussed in the first referenced paper indicated that the particle size should be less than about 100 microns and the experimental results attained were in general agreement with this prediction.
The process of the present invention obviates the rapid deactivation phenomenon described above while simultaneously, surprisingly, increasing the Viscosity Index (VI) and the yield of the lube oil product as well as reducing the pour point of the lube stock.